74 



VASCULAR CRYPTOGAMS 



development, the parenchyme of the fertile (apical) part of the leaf, 

 giving the appearance of a panicled or thyrsoid inflorescence. The 

 s_f>orange is usually stalked, and has an elliptical form, or that of a battle- 

 dore or racket-bat. The sides are commonly thin and membranous, and 

 the sporange dehisces either longitudinally or transversely, generally from 

 the elasticity of an anniihis or ring of brown thick-walled cells running 

 along or across it. The position of this annulus, and its more or less 

 complete development or entire absence, are useful characters in the 

 subdivision of the class. In the Marattiacese the sporanges are of 

 altogether different origin, being developed from hypodermal masses of 

 cells ; and transitional forms occur between the two. The spores are 



minute, very commonly re- 

 niform, or often nearly 

 cubical, resembling pollen- 

 grains in structure, usually 

 furnished with two coats, 

 an exospore and endospore, 

 the latter of which is some- 

 times double, and the 

 former generally marked 

 with papillae, reticulations, 

 &:c. 



A more minute descrip- 

 tion must now be given of 

 the structure and peculi- 

 arities of the various organs. 

 The great distinguishing 

 feature which characterises 

 the development of the 



Fig. 52. -Diagram of tip of leaf of Ceratopteris thalic- StCUl of fcmS, aS COntraStCd 



(Af(l?Kn°T"' '^' "'^'''''^ "^' ' ^' ^''^^'^' ^°^^ °^ ^^^^' ^^'^^^ ^^^^ which occurs in 



all Flowering Plants (Gym- 



nosperms and Angiosperms), is the presence of a single apical cell^ 

 from which the whole of the growing point or apical meristem origi- 

 nates, and which may therefore be recognised as the parent-cell of the 

 whole of the tissue subsequently formed. This apical cell is usually 

 wedge-shaped in creeping stems with a bilateral structure, a three-sided 

 pyramid in erect or ascending stems. The growing apex of the stem is 

 frequently completely hidden in the youngest leaf-bud, but in other species 

 there is a considerable intervening space. In some Hymenophyllaceae 

 leafless prolongations of the stem assume the appearance and the function 

 of roots. As contrasted with Flowering Plants, especially Exogens, the 

 stem of ferns is characterised by the small extent to which it branches ; 



